Glycerol substitutes



Patented June 22, 1948 GLYCEBOL SUBSTITUTES Karl Heinrich Walter Tuerck,Banstead, and Hans Joachim Lichtenstein, London, England, assignors toThe Distillers Company Limited, Edinburgh, Scotland, a British companyNo Drawing. Original application March 13,

1944, Serial No. 526,336. Divided and this application February 20,1945, Serial No. 578,950. In Great Britain November 27, 1942 10 Claims.(01. 175-315) This application is a divisional from our copendingapplication Serial No. 526,336 filed March 13, 1944.

It is known, for many purposes, to replace glycerol or ethylene glycolby aqueous solutions of sodium lactate.

These solutions have, however, the disadvantage that they attack certainmetals, especially aluminium or its alloys and corrode the surfacesespecially at those points at which two different metals-e. g.,aluminium and brass-are Joined together.

It is an object of the present invention to provide a solution which canbe used as a substitute for glycerol and which will not possess thedisadvantages attendant upon the use of sodium lactate.

when a solution of dl-beta-hydroxybutyric acid is neutralised in theusual way by means of an alkaline hydroxide or carbonate, the pH of thesolution thus obtained falls, on standing, due to the hydrolysis ofanhydrides of the acid. Even apparently pure sodiumdl-beta-hydroxybutyrate may develop acidity in solution.

Liquid compositions may, for example, be obtained by adding to asolution of dl-beta-hydroxybutyric acid, a suitable alkali (e. g. sodiumor potassium hydroxide, carbonate or bicarbonate) the amount of which issuch that the pH of the resulting solution remains within the pH rangesindicated. If desired, the addition of alkali can take place at raisedtemperature, e. g.

40-l10 0., at which hydrolysis of the anhydrides is rapid.

A small proportion of the above alkalis may be replaced by organicbases, e. g. triethanolamine or alkaline-reacting salts, e. g. trisodiumphosphate.

The liquid composition may contain, with advantage, small amounts, e. g.up to 3% by weight, of alkaline phosphates, silicates or chromates.Phosphates of amines, such as triethanolamine, which have beenpreviously proposed as stabilisers for polyhydric alcohols, areparticularly suitable for this purpose.

It is a further object of the inventionto provide a method of minimisingthe corrosion of a corrodible metal, as hereinafter defined, when incontact with water or an aqueous solution of an electrolyte.

The aqueous solutions of sodium or potassium dl-beta-hydroxybutyrate canadvantageously be used instead of glycerol in many, if not all, of

L its various applications and, at the same time,

do not cause any practical corrosion of parts formed of aluminium oralloys in which aluminium predominates nor do they cause any corrosionof parts in which aluminium is in contact with metals which themselvesare resistant to corrosion by water; this last fact is most surprisingsince these dl-hydroxy-butyrates must be regarded as being electrolytes.

By the expression corrodible metal used herein, is meant copper, brass,iron or nickel or alloys containing these metals, hard or soft solders,aluminium or alloys in which aluminium predominates. Where corrodiblemetals other than aluminium or aluminium are concerned, the pH of thesaid cll-beta-hydroxybutyrate solutions is, according to a feature ofthe invention regulated to fall within the range of 7.0 to 8.5,preferably '7.5 to 8.5.

Solutions containing 50% by weight of the salts do not solidify attemperatures as low as 50 C.

Solutions up to by weight can be boiled without decomposition and suchsolutions can be used in containers formed of metals of the character ofaluminium as the containers are not corroded. The same remark applies tocontainers which are lined with enamel. Such linings are corroded bysodium lactate which regularly develops an alkaline reaction.

The fact that sodium and/or potassium dlbeta-hydroxybutyrate reactsneutral in aqueous solution makes it especially suitable for electricalpurposes, e. g. in electrolytic condensers. In electrolytic condenserssodium and/or. potassium d1- beta-hydroxybutyrate is particularly.useful, as it can be made into solutions of high viscosity which haveconsiderable hygroscopicity which prevents the electrolyte from dryingout.

In the manufacture of the so-called dry electrolytic condensers it haspreviously been proposed to use a variety of salts in aqueous solutionas the electrolyte to which have been added thickening agents as well asother agents designed to prevent the electrolyte becoming useless byevaporation. The production of an electrolyte in this way is tedious andcostly. It has also been proposed to use metallic lactates aselectrolytes for this purpose. The lactates do not require the additionof thickeners and are sufliciently hygroscopic to avoid the necessity ofadding-substances to prevent evaporation of water.

We have now found that concentrated aqueous solutions of sodium and/orpotassium dl-betahydroxybutyrate adjusted so that their pH remainswithin the range 6.0-8.5 and.- preferably sodium and/or within the range6.0-7.5, are especially suitable for use as electrolytes in themanufacture oi electrolytic condensers. We have found that these saltsof dl-beta-hydroxybutyric acid possess an advantage over thecorresponding salts of lactic acid in that they are much less corrosivetowards the aluminium foils used in the condensers.

According to the invention therefore, there is provided an electrolyticcondenser comprising a plate, foil or the like of, or containing apredominating proportion of, aluminium and electrolyte consisting of anaqueous solution of potassium dl-beta-hydroxybutyrate whose pH has beenadjusted to remain permanently within the range of 6.0 to 8.5;preferably the pH range lies between the values 6.0 and 7.5 or, better,between 6.8 and 7.4.

Concentrated solutions of sodium and/or potassium dl-beta-hydroxybutyrate are of high viscosity so that the addition of thickening agentsor hygroscopic substances to prevent evaporation is not necessary.

' It is known that sodium lactate solutions become more and morealkaline particularly when in contact with aluminium surfaces andcorrosion of the aluminium takes place through an attack on the anodicoxide layer on the surface of the aluminium, which layer is necessaryfor the functioning of electrolytic condensers.

We have found that solutions of sodium and/or potassium dl-beta-hydroxybutyrates prepared in the above-described manner do not attack alumiriumand the pH of their solutions does not increase wtih age nor do suchsolutions cause debutyrate over sodium lactate is shown in the 101-.

lowing comparative examples:

Tests were carried out with equal amounts of by weight solutions of bothsalts by heating test-pieces to 95 C. for 50 hours in contact with thesolutions.

In the third test, sodium lactate attacked not only the aluminium butalso the brass, which remained entirely unaffected in the test withsodium dl-beta-hydroxybutyrate.

During the tests in the sodium lactate solution, the hydrogen evolvedwas visible to the naked eye.

A further series of .tests were conducted with pieces of metal and metalalloys having a surface of 1100 mm). The figures given show the loss ofweight (or where is shown the increase in weight) in mgm. per test pieceper 24 hours. The test pieces were immersed in the solution (whosecomposition is given in the table in percentage by weight) at atemperature of 80-90 C. and weighed at 24 hour intervals.

obppep Mild pH a it? m m as. is:

solder Solder 1 Sodiumlactate(30%) s5 65 2 Sodium hydroxybutyrate(27.5%) 6.8 nil nil nil 10.0 3 Sodiumhydroxybutyrate$27.5%)+Tricthanolamine phosphate 7.8 nil nil nil +0.5 0.9 1.0 0.2 4Sodiumhydroxybutyrate 27.5%)+Trisodium phosphate 8.4 nil 0.7 0.2 0.2 5Sodiumhydroxybutyrate (27.5%) 8.0 nil 0.4 0.2

struction of the protective oxide film in the condensers.

The electrolyte solution contains, preferably,- more than 40% by weightof the salt.

Solutions of more than 40% strength do not crystallise at temperaturesabove -20 C. and it is a special advantage of electrolytic condensersmade according to our invention that they do not deteriorate at lowtemperatures such as are ex- 5 .perienced, for example, in aircraft.

Compared with ethylene glycol, which has been used extensively in themanufacture of electrolytes for-condenser the solutions of the saidsalts vantage of non-toxicity and non-inflammability.

It is, of course, within the scope of our invention to employ, aselectrolytes, sodium and/or potassium dl-beta-hydroxybutyrate solutionswhich "of dl-beta-hydroxybutyric acid possess the adhave been modifiedby the addition of other ingredients such as gelatins, glycerol orethylene glycol.

A special advantage in the use of sodium and/ or potassiumd-l-beta-hydroxybutyrate solutions lies in the fact that they can bereadily obtained from distilled dl-beta-hydroxybutyric acid and thus befreed from inorganic impurities such as chloride, which are a frequentcause of deterioration in electrolytic condensers.

5Q the action of a. 30% by weight aqueous solution of sodiumdl-beta-hydroxybutyrate at C. The following table shows the loss ofweight in gms.

per sq. metre over that period.

Mild steel- Aluminsolt solderbmss lum pH 6.8 1.12 None. pH8 None Do. pH7.6 (+triethanolamine phosphate do Do. pH 7.8 (-l -trisodium phosphateo.5%) .do.---- Do.

The advantage of sodium dl-beta-hydroxybutyric acid, e. g. as obtainedby the oxidation of desired amount of water. It is, however, alsopossible to wash the solid residue with cold alcohol, though therecrystallisation from alcohol gives a still purer and exactly neutralproduct. The dlbeta-hydroxybutyric acid used may have been previouslydistilled in vacuo in order to facilitate the production of a pureproduct.

In contrast to the case of sodium lactate? the direct oxidation ofacetaldol to the acid, as indicated above, offers the further advantagethat it is possible to obtain a substantially water-free acid and thismerely requires to be diluted with the necessary amount of water andtreated with the required alkali in order to give the desired solutions.Thus the arduous evaporation of water from primary dilute solutions,such as are unavoidably obtained in the manufacture of sodium lactateand which leads to the formation of deeply coloured solutions, isavoided. Unlike sodium lactate the sodium or potassium salt of thedibeta-hydroxybutyric acid will form solid well defined crystals by thesimple evaporation of its aqueous solutions and, therefore, it canreadily be purified by dispersing it in a solvent in which said salt isinsoluble or only sparingly soluble.

We have discovered that there is yet a further advantage in that if asolution of the dl-betahydroxybutyric acid in water is prepared with aconcentration greater than 35% by weight of the acid, the process forthe preparation of the sodium salt is made very much simpler since wehave discovered that with such solutions it is possible to add an excessof sodium or potassium carbonate since the excess unreacted sodium orpotassium carbonate will not dissolve, or only very slowly dissolves, inthe aqueous solution of sodium dl-beta-hydroxy butyrate; thus all thatis necessary is to prepare the sodium salt by the conduits through whichthey may be passed when the solution is used under conditions in whichcrystallisation is likely to take place, although under normalconditions crystallisation does not occur.

If, however, the possibility of crystallisation is present and isthought to be undesirable, it may be counteracted, without detriment tothe other properties of the solution, by the addition of small amountsof the lower sugars; we have found that the addition of these lowersugar substances inhibits the crystallisation of solutions of the sodiumsalt. It is therefore a further additional feature of the invention toprovide aqueous solutions of the sodium dl-beta-hydroxy butyratecontaining small amounts of the lower soluble carbohydrates orsubstances derived therefrom. We find that the oxidation of technicalacetaldol is a. particularly advantageous method of obtaining thedesired solutions of the sodium salt since acetaldol contains suchsubstances as will form, in the final oxidation mixture, smallquantities of the lower sugars and this invention therefore contemplatesthe use of such solutions for the formation of the sodium salt of theinvention from which'the lower does not attack the acid and thereafterneutralise sugar compounds have not, or have only partially, beenremoved and in which the pH value is preferably maintained between 6.5"and 7.0 in order to prevent the formation of colour in the solution withage or with use.

We find that solutions of sodium dl-betahydroxybutyrate aremoreeffective weight for weight as freezing point depressants than aresodium lactate or other anti-freeze agents.

This may be seen from the following table in which there is set out theweights per cent of various anti-freeze agents necessary to reduce thefreezing point of an aqueous solution to a value Of -20 C.

Anti-freeze agent Percentage by weight Glycerol 45. 0 Ethylene glycol.38. 0 Sodium lactate 32. 5 Sodium dl-beta-hydroxybutyratc. 27. 5

It has been observed that the solutions of the present inventiondevelop, at low temperatures, a lesser viscosity than that of anotheranti-freeze solution of the same freezing point, i. e. the solutions areless viscous at low temperatures than the corresponding glycerolanti-freeze solutions whilst at high temperatures the viscosity of thesolutions is little different from that of water.

The solutions of the present invention have a boiling point only alittle higher than that of water, for example, a 50% by weight solutionhas a boiling point of only 108 C.; the heat capacity of solutionshaving a freezing point of -20 C. or less is high 1. e. the specificheat of such solutions is about 0.9 calorie per gram. The solutions arealso very stable to heat and solutions of from 10-40% by weight remainneutral even if boiled 'for many hours whereas solutions of sodiumlactate develop an alkaline reaction which becomes more pronounced asheating continues.

Where substantially colourless solutions of sodiumdl-beta-hydroxybutyrate are desired it is preferable to remove anyaldehyde or high molecular weight compounds by treating the aqueoussolution of the dlbeta-hydroxybutyric acid with active carbon and/orhydrogen peroxide or other bleaching agent, such as basic lead acetate,which the acid with alkali asalready described. It is also advisable toheat the reaction mixture, obtained by the oxidation of acetaldol, withlive steam until all volatile aldehydic substances are removed andthereafter to add alkali to form the sodium dl-beta-hydroxybutyrate. Itis observed that the acid remains in the still unchanged throughout thesteam distillation.

What we claim is:

1. An electrolytic condenser comprising an electrode of a materialcomprising essentially aluminium and an electrolyte consisting of anaqueous solution of a salt of the group consistfing of the sodium andpotassium salts of dlbeta-hydroxybutyric acid, the pH of said solutionbeing substantially permanent between 6.0 and 8.5.

2. An electrolytic condenser according to claim 1 wherein the pH of theelectrolyte solution is between 6.0 and 7.5.

3. An electrolytic condenser according to claim 1 wherein the pH of theelectrolyte solution is between 6.8 and 7.4.

4. An electrolytic condenser according to claim 7. 1 wherein theelectrolyte solution contains not less than 40% by weight of said salt.

5. An electrolytic condenser comprising an electrode containing at leasta predominating proportion of aluminium and an electrolyte consisting ofan aqueous solution 01' an alkali metal salt of dl-beta-hydroxybutyricacid whose pH is substantially permanent between 6.0 and 8.5.

0. .An electrolytic condenser according to claim 5 wherein the pH of theelectrolyte solution is between 8.0 and 7.5.

7; An electrolytic condenser according to claim 5 wherein the pH of theelectrolyte solution is between 6.3 and 7.4.

8. An electrolytic condenser according to claim 5 wherein saidelectrolyte solution contains not less than 40% by weight of sodiumdl-betahydroxybutyrate.

9. An electrolytic condenser according to claim 5 wherein saidelectrolyte solution contains not less than 40% by weight of potassium(ll-betahydroxybutyrate.

10. An electrolytic condenser comprising an electrode of a corrodiblemetal and an electrolyte 8 consisting of an aqueous solution or analkali metal salt of dl-beta-hydroxybutyric acid whose pH issubstantially permanent between 6.0'and KARL HEINRICH WALTER TUERCK.HANS JOACI-HM LICH'I'ENSTEIN.

REFERENCES CITED The following references are of record in the OTHERREFERENCES Annalen, vol. 149, pp. 210, 211 (1869). Kolthofl et al.,Recueil 'Irav. Chem. de Pays Baa, vol. 46, pp. 36, 37 (1927).

